Please Help!! Trans or sensor?

Sometimes my 95 sc Riv doesn't shift into OD. Sometimes the service engine soon light comes on. These two things do not necessarily coincide. I just had the trans fluid and filter changed, thinking this would help. I can't tell any difference in how the car shifts (or doesn't). I had the transmission re-built approximately 2 years ago which cost me $1100. I was thinking a rebuilt trans. should last a little longer.
The guy at Cottman is telling me I need to have it rebuilt again at around $1600. It just makes no sense to me that, if the trans really were going bad, that the car would drive and shift so normally part of the time, and then run 60 mph at 4000 rpm the other part of the time. Anyone had this problem?

it really depends on what was done during the rebuild. Some places don't charge much because they resuse most of the parts. Things like soleniods can get sticky or sloppy over time and cause these types of issues.

Another thing to keep in mind is that the TPS is directly related to the shifting of our transmissions. You mention getting a check engine light, what codes are currently stored? To possibly help you solve the issues or diagnose them better, we'll need those codes and your assistance.

I don't think the '95 is as code/transmission friendly as our newer ones Bill. Does the trans even throw codes on '95s?

I had a very similar problem with my '98. The SES light came on, throwing codes for a sticking TCC solenoid. Eventually the problem got worse until I had no OD (TCC lock-up) at any time. This didn't hurt the transmission as long as I didn't drive it long distances, and being colder out helped. I drove my normal 30 min-each-way work commute every day for 3 months with no problem. Then on Christmas Eve (it was a warm 50ºF that day) I took a 400 mile trip and the fluid just cooked from the heat. Engine was fine, but I ended up needing a re-build. I think if I had changed out the fluid before the trip, it might've been fine.

My advice to get those codes read. If it's TCC related, keep an eye on that transmission fluid and have it changed frequently, or if it looks brown or smells burnt. Drive the car as long as you can. When it finally goes, you can decide if it's still worth paying that $1600. In my case, it cost me a little more, but they said it would've been a lot anyway to fix the solenoid and replace the valve body back at the first sign of trouble. Hope this helps, and good luck.

Like the others said, it can be a number of things - brake pedal switches improperly adjusted (always on), TCC solenoid failed (easy fix in the pan), TCC clutch worn out (must remove trans and replace TC).

Please get the codes scanned and report back.

I had an after factory sound system installed in my Riviera. I had the same problems that you are expieriencing shortly after. I was told by my mechanic that it was an electrical issue due to the way my sounds were hooked up. My car was hooked up for a diagnostics check and no problems were found. Dont know if this helps you or not just thought I'd share.